diff --git a/python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPublic.qll b/python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPublic.qll
index 49cf972ab04..a0414eba817 100644
--- a/python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPublic.qll
+++ b/python/ql/lib/semmle/python/dataflow/new/internal/DataFlowPublic.qll
@@ -400,7 +400,7 @@ class ModuleVariableNode extends Node, TModuleVariableNode {
   override Scope getScope() { result = mod }
 
   override string toString() {
-    result = "ModuleVariableNode in " + mod.toString() + " for " + var.getId()
+    result = "ModuleVariableNode in " + concat( | | mod.toString(), ",") + " for " + var.getId()
   }
 
   /** Gets the module in which this variable appears. */